Astronomical seeing: to be clear or not so clear

Weather apps may provide accurate information, but perhaps not the information amateur astronomers are looking for.

Credit: iStock

When the weather forecaster makes the statement "tonight will be clear" or "will have clear spells" I have no doubt that astronomers all over the country get excited.

Yet what constitutes a clear sky to the weather forecaster may not really be what we astronomers would prefer, which is an actual cloud and haze-free night sky.

You see a thin layer of haze can still look clear to most people, but seasoned veterans may look up and see even stars high up in the sky twinkling.

They will shake their heads sadly and remain indoors.

Such occasions are a good time to clean or service equipment, as astronomers know the view through a moderate-sized telescope will show the stars slightly blurry whilst detail on the planets may well be lost.

Faint deep-sky targets become impossible to view and as such it’s even possible that newcomers to visual astronomy may well be disappointed and put off by the poor view.

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